Catalytic cracking



Feb.`29, 1944. Q THOMAS CATALYTIG CRAGKING Filed April 8, 1941 .ffwweyf Patented Feb. 29, 1944 y 2,342,984 CATALYTIC CBACKING Charles L. Thomas, Chicago, Ill., asslgnor to Universal Oil Products C ompany, Chicago, Ill., a

corporation of Delaware Application April 8, 1941, Serial No. 387,470 4 Claims. (Cl. 196-52) This invention relates to a process for converting hydrocarbon oils to high yields of gasoline of high anti-knock proportion and is a continuation-in-part of my co-pending application Serial No. 291,892, flied August 25, 1939, which in turn was a continuation-in-part of my application Serial No. 273,236, filed May 12, 1939, now Patent No. 2,286,447, dated June 16, 1942. More speciilcally the invention concerns a method of manufacturing motor fuels from petroleum sources although hydrocarbon oils from other sources may also be used.

Although the process may apply to theproduction of motor fuels for use in any type of internal combustion engine, it finds special application in the manufacture of fuels for use in airplane motors. This is true because of the highly stable character of the finished product as well as its great susceptibility to increase in octane number by the addition of tetraethyl lead.

Numerous processes have men developed for the production of increased yields of motor fuel from crude petroleum and other hydrocarbon sources. Among these is the non-catalytic thermal cracking process whereby heavy oils are converted to substantial yields of gasoline haying relatively high antiknock value. Straightrun gasoline and naptha which may have relatively poor antiknock properties are non-catalytically reformed to produce gasoline of improved octane number. cracking processes yield substantial quantities of gases containing polymerizable olens, and various polymerization processes may be used in commotion therewith to augment the yields of valuable motor fuel produced. Y

Among processes of more recent development are catalytic cracking processes wherein hydrocarbon fractions containing substantially no gasoline are converted to high yields of premium grade motor fuel.

The octane numbers obtainable by commercial non-catalytic cracking and reforming processes are relatively limited, since improved antl-knock properties beyond a certain point can be gained only at the expense of yield of gasoline, and eventually a point is reached wherein it is no longer economical to increase the octane rating in this manner. Catalytic cracking and polymerization processes ymay be used to produce motor fuel of higher octane rating than is economically feasible according to the noncatalytic method of operation.

The present invention relates to improvements The reforming and Y,

in methods of manufacturing high anti-knock value gasoline from crude petroleum oils and especially to a combination of cooperative steps wherein substantial yields of gasoline are produced at relatively mild temperature conditions with a highly active catalyst, while further yields of gasoline are produced from the more refractory insufnciently converted fraction from this step in contact with the partially spent catalyst which is still suitable for cracking at somewhat higher temperatures. Moreover, the process permits the use of so-called dirty oils rather than selected distillate fractions which are necessary for many existing catalytic cracking processes. The overall resuit ls increased yields of improved anti-knock gasoline.

In one specific embodiment the present invention` comprises a method for producing high anti-knock motor fuel from hydrocarbon oil which consists in mixing a portion of said oil with a powdered cracking catalyst, heating the mixture to a temperature of 50G-900 F. under a pressure of 50-1000v pounds per square inch, passing the mixture into a vertical reactor containing bubble trays, perforated pans or other type of contacting members which assist in contacting upwardly rising vapors with downwardly flowing liquid-catalyst suspension, removing gasoline and gas overhead from said coritactor, withdrawing insuiciently converted oil containtaining suspended catalyst from the base oi' said reactor, passing the mixture to a cracking zone comprising a tubular heater followed by a reaction chamber at a temperature within the range of approximately 800-1200 F. and a pressure of approximately -1000 pounds per square inch, passing the reaction products containing suspended catalyst into a flashing zone, withdrawing a portion of oil unsuitable for further conversion containing suspended catalyst, recovering and reactivating the catalyst, removing the vapors from said ashing zone and passing them with or without added heat to the aforesaid catalytic reactor at a point be- `low the point of introduction of the original hydrocarbon oil and catalyst mixture.

The charging stock which may be converted according to the present process is suitably topped crude oil although crude oil itself or various fractions thereof, such as gas, oil, kerosene distillate, etc., may also be used.

The vertical contactoamay be operated at a temperature of approximately 50G-900 F. and a pressure suiiiciently high to maintain the tem-- perature at the point of entry of the hydrocarbo catalyst mixture within the specified reaction range while removing a product of-r the desired end point overhead. Distillates of higher end point than gasoline may be removed from the reactor and separately fractionated to the desired end point in such cases as this procedure is most practical. The pressure in the contactor may be within the range of 50-300 pounds per square inch and is normally of the order of 50-200 pounds per square inch. The point of entry is normally approximately midway in the tower. The upper section of the contactor is a conventional type of fractionator suitably consisting of a series of bubble trays. The lower section may be a series of bubble trays or other equivalent contacting members such as perforated pans, side-to-side baffles, etc.

The apparatus for the higher temperature cracking step may comprise any conventional type of non-catalytic cracking plant consisting essentially of a tubular heater followed by a reaction chamber and a flashing zone and operated under conditionsv of temperature and pressure usual in such equipment, namely, 8001000 F. and 100-1000 pounds per square inch.

The catalytic mixture after use at the relatively low temperature conditions existing in the vertical reactor loses some of its activity but is still sufficiently active at slightly higher temper atures to cause substantial conversion of heavier hydrocarbon oils into gasoline having a relatively high olefin content and a high antiknock value. This gasoline together with other readily Vaporizable materials of higher than gasoline boiling range is returned to the vertical reactor wherein the olefin containing gasoline is converted into a substantially olefin-free product. If additional heat is needed in the vertical contactor, this can be supplied by heating the vapors from the flash chamber prior to their introduction, into the vertical contactor.

The spent catalytic mass is separated from the flashed residues by any suitable means such as filtering,l settling, etc. The powdered catalyst may also be washed with a solvent such as cracked gasoline to remove the maior portion of the residue remaining thereon. The catalyst is then reactivated by heating in the presence of an oxygen containing gas at a temperature in excess of approximately 1000 F..

As a further variation a liquid side cut of greater than gasoline boiling range may be withdrawn from the upper portion of the contactar, mixed with a portion of the powdered catalyst and returned to the contactor at a point above that at which the original charge is introduced. In this way additional contacting of the upwardly rising hydrocarbon vapors with the cracking catalyst can be obtained.

The catalysts. which are useful in the present process may include cracking catalysts of various types, such as synthetic precipitated composites consisting essentially of a major portion of precipitated silica having added thereto relatively minor portions of precipitated refractory oxides to form masses consisting of silica-alumina, silica-zirconia, silica-alumina-zirconia, etc., said composites being substantially free of alkali metal compounds.

In the following specification the terms silicaalumina, silica-zirconia, and silica-alumina-'zirconia masses are used in a broad sense. Inasmuch as the chemical knowledge ofthe solid state has not been developed perfectly, it is not posthe motore of all solid substances.

All that can be said definitely concerning these masses is that they contain silicon, oxygen, aluminum, and/or zirconium in combination. Gen- 5 erally speaking, however, all these components indicate more or less low catalytic activity individually but in the aggregate display high activity. 'I'his activity is not an additive function, it being relatively constant for a wide range of proportions of the components, whether in molecular or fractions of molecular proportions.' No one component can be determined as the one for which the remaining components may be considered as the promoters according to conventionalv terminology, nor can any component be determined as the support and the others the catalyst proper.

According to the description of the preparation of the preferred catalysts given below, precipitated hydrated alumina and/or hydrated zirconia are composited with hydrated silica gel, otherwise known as silica hydrogel, and then the composite is washed, dried, and calcined, producing-a catalytic mass. However, the different 2s catalysts which may be so produced therefrom do not necessarily give equivalent results.

A large number of catalysts which havel been `developed to assist in thermal cracking' of hydrocarbon oils tend to accelerate the formation of gas so rather than gasoline. Among these are the reduced metal catalysts, such as nickel or iron. A further characteristic of this type of catalyst is that poisoning by sulfur occurs and the catalytic surfaces are rendered inert by coatings of carbonaceous material.

The preferred catalysts of this invention are characterized by selectivity and by accelerating gasoline-forming reactions, rather than gas and carbon-forming reactions, by their refractory 4o character which enables themV to retain their catalytic activity through many repeated periods of use' and reactivation under vsevere conditions of temperature, and by the ease and simplicity of manufacture and their exact reproducibility.

T'he finished catalytic masses contain alumina and/or zirconia in amounts varying over a considerable range, for example, from 1 to 30 weight per cent and are preferably of the order of a'pproximately 5 to 30 weight per cent of the compound calculated as A120; or

The present catalytic mass' may be prepared according to a number of alternative methods which will be discussed in a general way in the following description. Brieny, the method involves the precipitation of hvdrogels of silica and the added compound, either simultaneously by co-precipitation methods, or by separate precipitation of the hydrogels, such a manner as to produce a more or less uniform mixture, or by the successive precipitation of silica hydrogel and the added alumina and/or zirconia hydrogel constituent. l

A preferred method` of preparation is to precipitate a silica hydrogel by the addition of an acid to a solution of water-soluble silicate. The precipitation of the silica 'gels should be can'ied out under controlled conditions in order to produce material which, when vcomposited with alumina and/or zirconia as hereinafterdescrlbed, results in `a catalytic mass of a high degree of activity. In general, when precipitating silica' gel from solutions of sodium silicate, it is desirable to add ysuiilcient acid to cause complete gel forma-l tion. If the excess of acid used exceeds approximately 20%, the precipitated hydrogei becomes followed by mixing inlproperties are lost.'

throughline 50, valve I Yaudline 52 .to reactor 23,

extremely dimcult to ltcr, and its more desirable After' precipitation, the silica gel is preferably washed free of soluble salts. This may be done by washing the hydrogel with dilute solutions'of a mineral' acid, such as hydrochloric acid, or with water containing small amounts of ammonium v chloride orY aluminum chloride.

' lytic in character. It may also be possiblev that other reactions of an unknown character such as the catalyzing of undesirable reactions by alkalimetal components may account for the observed detrimental effects. Whatever the explanation. we have observed that the removal of alkalimetal compounds lis of primary importance and our preferred catalysts are of this nature.

The accompanying drawing illustrates diagrammatically'one embodiment of the present invention. The drawing has not been made to scale nor has any attempt been made to proportion the equipment exactly. It should not be construed to limiting the invention to the exact equipment given therein.

Referring to the drawing the crudeA oil charged enters through line I,` valve 2 and pump 3. A portion of the oil is pumped throughv line 4 and valve 5 into slurring pot 6 wherein it is mixed by means of agitator 1, with powdered catalyst from catalyst storage 8 which enters through'line 8 and valve I0. The slurry passes through line II, valve I2 to line l5 where it meets and mixes with the remaining portion of charging stock from line I3 and valve I4. The mixture passes through valve I6, pump I1 and valve I8, coil I8, which is disposed in heater 20, where yit is heated to a temperature within the range of 50o-900 F. and a pressure of approximately 50 to 1000 pounds per square inch. The heated mixture passes through line 2l and valve 22 to reactor 23. The upper part of this reactor is a fractionating section. Gas and gasoline are removed overhead through line 24 and valve 25 through suitable stabilizers. heat exchangers, condensers, etc., not shown. The insufliciently converted oil containing suspended catalyst passes downwardly through the reactorthrough line 26, valve 21. pump 28, valve 28 to coil 30 which is disposed in heater 3|. Line 32 and valve 33 serve as a means of removingr a part or all of the mixture from the system. The heated mixture at a temperature of approximatelyo to 1200 F. and a pressure of 100 to 1000 pounds per square inch passes through line 34, valve 35 to reaction chamber 36, wherein additional conversion to gasoline and gas occurs. Reaction products leave through line 31 and valve 38 entering flash chamber 39 wherein the pressure is substantially reduced. A fraction of residue unsuitable for further con- 'version passes through line 40 and valve 4I to separator 42. lSpent catalyst is removed through line 43 and valve 44 to reactivator 45 and thence by means of line 46 and valve 41 to catalyst storage 8. The cracked residue which may be used entering the reactor. at ay pointr below that` at which the original oilv is introduced. If additional heat is needed, :a portion of the oil may be passed through line53, valve 54, coil 55,1which is-disposed in heater `56 and through line 51 and valve..

' 58 ,to line 52 and thence to reactor 23.

According to Aone alternative the flash chamber 38 pass through line 1I and valve 12 `to separator 13, where the normally. gaseous hydrocarbons with or withoutthe gasoline fraction are separated and removed from the systern through line 14 and valve 15. In this manner they are then taken to suitable stabilizers. heat exchangers, etc., and may be separated into a. fraction which may be further treated by such methods as polymerization,` alkylation, etc., to produce valuable by-products. The higher boiling hydrocarbons with or without the gasoline are then removed from the bottomV of separator 13, through line 16, valve11, pump 18, line 53, valve 54 and coil 55 wherein the temperature is raised to a suitable point within the range of approximately 650-900 F. The products then pass through line 51,.vaive 58 and line 52 to reactor 23. l

.According to another alternative method the reaction chamber 36 may be by-passed and the oil-catalyst mixture from line 34 may be passed -through line 58 and valve 60 toash chamber v39.

- Under certain conditions it is advantageous to introduce powdered catalyst into the upper section of the fractionating column in order to provide additional treatment of the upwardly flowing vapors. This may be done by withdrawing a portion of the oil through line 6I, valve 62, heat exchanger 63, into slurry pot 64 where it is mixed with powdered catalyst from line 65 and valve 66, which is maintained in suspension by means of agitator 61. The slurry passes through line 68, valve 69 and heat exchanger 10 to reactor 23, entering at a point above that at which the original hydrocarbon charge is introduced.

According to another alternative, a portion of the hydrocarbon oil charging stock may be passed through line I, valve 2, pump 3, line I3, line 18, valve 80 to line 26 where it commingles with the suspension of cracking catalyst in insuiciently converted oil from line 26 andv valve 21. The mixture passes by previously described routes to coil 30 and thence to reaction chamber 36. etc. n

This particular operation has the advantage that 43. The vapors from flash chamber 38 pass a part or all of the original charging stock may be passed to the high temperature cracking step without first being introduced into the lowy temperature catalytic reactor. When operating in this manner a portion of the charge may be used to form a slurry with the catalyst prior to introducing it into catalytic reactor 23. If all of the charge is passed through line 18, etc., the powdered catalyst may be introduced in the previously described manner from slurry pot 64.

The following example is given to illustrate the usefulness and practicability of the invention but should not' be .construed as limiting it to the exact conditions given therein.

A Mid-continent topped crude oil was made into a slurry with a powdered cracking catalyst. The catalyst was a composite of parts preciptated silica having added thereto 8 parts of precipitated alumina and 4 parts precipitated zirconia under conditions such that the comvapors from l tower.

reactivated by heating in the posits was substantially free of elken-metal ions. The mixture of Aoil and suspended catalyst was '-=.fh'eated to a temperature oi' '150 F. under a pres- ,sure of 100 pounds per square inch and passed gaswere removed overhead and the insumcient- 1y converted oil containing the catalyst in suspension was withdrawn from the bottom of the The' mixture was .pumped through a heating coil at a pressure of 500 poundsper square inch and a temperature of 930 F. It i5 was then passed into the reaction'chamber of\` a conventional cracking unit where additional cracking took place. The conversion products were passed from the reaction chamber to a flash 4 chamber wherein the pressure was reduced to approximatelyl 150 pounds per square inch. A

.cracked residue containing catalyst in suspension was withdrawn from the system and the catalyst was recovered by ltration. It was then presence of oxygen to burn oil' carbonaceous deposits and returned for further use in the process. The vapors from the iiash chamber wereV removed and returned to the lower section of the catalytic reactor, the point of introduction being well below that at which the original raw oil'charge was introduced. In this manner gasoline vapors and gas passed upwardly through the descending olif-catalyst suspension and the gasoline was converted into a substantially olefin-free, high octane number motor fuel. A total yield of of 400 F. end point cracked gasoline having an octane umber of 78 was produced in this manner. The octane number was increased by the addition of 6 cc. tetraethyl 1aed per ganen to 94.5. The 40 bromine number of the gasoline was 3, and the sulfur content was 0.03%.

I claim as my invention:

1. A hydrocarbon oil conversion process which comprises passing the chai'ging oil, together with powdered cracking catalyst. in a restricted stream through a heating zone and heating the mixture therein to a catalytic cracking temperature under superatmospheric pressure, \.\introducing the heated mixture at an intermediate point in the heightV of a vertical reaction zone maintained under catalytic crackingconditlons and therein eiecting substantial cracking oi the oil, separat- 4ing vapors from the mixture in said reaction zone and passing unvaporized portions of the mixture, including the powdered catalyst, downwardly through the lower portion of the reaction zone, then removing admixed unvaporized oil and catalyst from'the reaction zone and cracking the unvaporized oil in the presence of said catalyst at a higher temperature than is maintained in said reaction zone and adequate to produce oleilnic gasoline from the unvaporized oil, introducing., vapors of oleflnic gasoline thus formed to the reaction zone substantially below said intermediate point to pass upwardly in countercurrent contact with the descending unvaporized oil and catalyst, converting the olenic gasoline .to a substantially olefin-free product during its upward passage through the reaction zone, and removing a substantially olefin-free gasoline from the upper portion of the reaction zone.

2. 'I'he process as defined in claim 1 further characterized in that said unvaporized oil is cracked at a temperature in the approximate range of 800 to 1200l F.

3. The process as deilned in claim 1 further characterized in that vaporous products o1' the higher temperature cracking step, including gasoline and heavier fractions, are introduced to said reaction zone.

4. The process as defined in claim 1 further characterized in that said olenic gasoline, prior to introduction to the reaction zone, is separated from conversion products boiling outside the gasoline range.

CHARLES L. THOMAS. 

